From the article, it seems clear they want to start their own thing. "Amazon’s goal is to eventually haul and deliver packages for itself as well as other retailers and consumers—making it a direct competitor with UPS and FedEx, according to people familiar with the matter. "
The question is will they pay their drivers and sorting facility workers as much as UPS and FedEx. A UPS driver makes $25-$30 which isn't a bad gig, and FedEx pays around the same. Even a part time sorting job is a pretty good job for a college student.
It'd be interesting if they took over one of the carriers they've contracted with (ATI or Atlas). The company is vehemently against organized labor, yet both companies have unionized pilot groups.